1. Field of the Invention
This invention relates to vacuum or suction cleaners and more particularly to high efficiency vacuum cleaners, preferably incorporating multiple filter stages and in which the initial filter stage is self cleaning by reason of the use of a particularly designed relatively coarse mesh filter material positioned over a debris or particulate collection chamber, preferably containing an impervious dust or particulate collection bag.
2. Description of the Prior Art
A large number of so called vacuum or suction cleaners have been designed in the past. Such cleaners have usually involved the use of rotary fan means to either draw dust laden air through a filter medium such as a cloth bag or the like or to blow dust laden air into a filter such as a filter bag. Particles of dust or other debris are caught by the filter material while air passes through the filter material. As additional dust and debris is built up on the filter material the pores or openings in the filter become partially blocked with dust and other particulates. The resulting accumulation of dust itself becomes a filter of sorts and the efficiency of the filter action at first increases. Beyond a certain point, however, the efficiency of the filter decreases as the filter medium becomes more impervious to air due to a thick layer of dust and other debris accumulated on the surface of the filter. Multiple stage filtering has been used to increase the efficiency of filtering and the length of the filtering cycle, i.e. the length of time between cleaning or emptying the filter. The initial filter medium in such arrangements is usually coarser, or in other words, has larger holes or meshes in it, than subsequent filters. The dust accumulated is in such multiple stage filtering arrangements distributed between the multiple filter mediums with the larger particles being collected on the coarser initial filter medium or mediums and the smaller particles being caught on the finer filter medium or mediums. This extends the filter cycle of all the filter mediums, but is not always worth the trouble, since there are then more filters to be changed less frequently rather than less filters to be changed more frequently and the trade off is not always advantageous. Of course, the filter stages can be arranged so that the mesh size of one or more of the filters is such that the particular filter accumulates more than its share of particulates and dust so only one filter at a time usually has to be changed or cleaned. This, however, essentially defeats the original aim of increasing the number of stages in the filter cycle.
Some vacuum or suction systems have provided cleaning means such as scrapers, rappers, backflow systems and the like to aid in cleaning the filters and particularly an initial coarse filter, but such arrangements add considerable complication to the apparatus. Thus, while the filter cycle may be lengthened, the extra expense and complication is a considerable disadvantage. In addition, scrapers and rappers sometimes tend to force dust and dirt through the mesh of the filter causing an overall decrease in filter efficiency. Such systems also tend to remove a large proportion of the accumulation of dust from the filter surface so that a new layer of dust must accumulate before efficient filtering can take place. Some scrapers are arranged only to remove a certain proportion of the dust accumulation by passing the scraper along the filter at a predetermined distance from the filter surface. However, this type of arrangement tends to compact the remaining particulate accumulation on the filter at the same time and this interferes with the efficiency of the filter. Backflow type arrangements which periodically force dust layers from the filter surface are inefficient since the vacuum or suction filtration cycle cannot operate while the backflow is operating and the time available for actual cleaning or suction is thus considerably decreased. While a judicious selection of filter stages may alleviate many of the above enumerated difficulties, the principal difficulty of intermittent operation due to the necessity of periodically cleaning one or more of the filters remains. The following U.S. patents are examples of the stage of the prior art as described above.
U.S. Pat. No. 2,198,568 issued Apr. 23, 1950 to E. H. Yonkers discloses a self cleaning suction cleaner which uses a filter medium sold under the name of Dextilose. The filter material is treated with viscose to form a smooth satin finish. The viscose coating prevents adhesion of dust to the filter medium so that "a heavy accumulation of dust and dirt is not possible, the dust and dirt flaking off from the action of gravity aided by the draft of incoming air and falling into the container below." The filter thus tends "to maintain itself in a clean condition."
U.S. Pat. No. 2,295,984 issued Sept. 15, 1942 to B. C. Wilson discloses a shop type vacuum in which air enters a canister where it drops out a considerable amount of its particulate matter which is thereby removed and the air then passes upward into an inverted filter and removes additional particulates. The filtering cylinder or bag collapses each time the cleaner is shut off so the accumulation of dirt falls into the lower portion of the canister leaving the filter bag free to pass a maximum amount of air when the cleaner is again activated.
U.S. Pat. No. 2,713,921 issued Jul. 26, 1955 to J. Turner discloses a filtering arrangement in which a spiral wiping bar wipes the inside of a cylindrical filter medium to remove accumulated dust. The wiping spiral leaves a sufficient build-up of particulate material on the filter to allow the filtering of finer particles to continue. Turner is only one example of a large number of prior devices for physically removing dust from filter surfaces.
U.S. Pat. No. 3,653,189 issued Apr. 4, 1972 to Y. Miyake, et al. discloses a two-stage filter vacuum cleaner. The initial discussion in the patent discloses that in order to allow a longer vacuum period it has previously been known to use a two-stage filtering system comprising a dust collecting receptacle with a filtering screen of relatively large mesh size and a second fine mesh size filtering medium located immediately down-stream from the first course filtering screen. The invention of the patent involves a two-stage filtering arrangement including a first course filter screen made of plastic material, fine metal wires or the like and having a relatively large mesh size. Immediately behind is a main filtering means comprising a filter cloth having a fine mesh size which collects the finer dust particles. Also disclosed is a vibrator for use in shaking the dust from the main filter cloth.
U.S. Pat. No. 3,609,946 issued June 28, 1968 to H. Nakagawa et al. discloses a two-stage electric suction cleaner including a relatively coarse mesh filter and a finer mesh filter. As disclosed the coarse filter is less susceptible to clogging and the finer mesh filter does not have to handle as much dust as it would in the absence of the coarse filter. The period of cleaning is thus increased. As disclosed, the size of the holes, particularly in the coarse filter, is closely related to the period of efficient dust collection. This relationship is shown in the graph in FIG. 8 of the patent. FIGS. 10, 11 and 12 disclose a dual arrangement including two concentric bag or cylinder type filter means.
U.S. Pat. No. 3,653,190 issued Apr. 4, 1972 to W. J. Lee et al. discloses a vacuum cleaner arrangement including a lower canister which may be lined with a plastic bag or bags to receive detritus dropped from a series of upper filter mediums. A vacuum arrangement is provided in the walls and bottom of the canister to hold the plastic bag against the sides of the canister.
U.S. Pat. No. 3,835,626 issued Sept. 17, 1974 to Y. Miyake, et al. discloses a two-stage vacuum cleaner incorporating a first relatively coarse mesh adjacent a dust storage chamber followed by a conventional cloth filter which accomplishes the final filtering of fine dust particles. The initial filter screen may be made of plastic materials, fine metal wire, or the like and has a relatively large mesh size. The second filter means is in the form of a dust collecting bag made from cloth or the like for collection of fine dust particles. The two-stage filtering arrangement provides longer time periods between filter cleaning cycles.
While prior devices such as shown in the Yonkers U.S. Pat. No. 2,198,506, where the filter medium is smooth and non-adherent so large accumulations of dust cannot form, and the Wilson U.S. Pat. No. 2,295,984 where the filter collapses at the end of a suction cycle causing dust to be ejected, are in effect self cleaning, such devices have not proved completely satisfactory since in most cases too much dust is removed, seriously decreasing the efficiency of the filtering action and in the case of the Wilson arrangement the filter cleaning cycle only occurs when the filtering cycle is interrupted.
It is a primary object of the present invention, therefore, to provide an industrial vacuum type cleaner which is substantially self cleaning.
It is a further object of the invention to provide a multiple stage vacuum cleaner which can be used for the collection of extremely fine or toxic, acid or otherwise dangerous materials.
It is a still further object of the invention to provide a combination of filter cycles and a filter arrangement whereby toxic materials can be deposited in a closed bag or other receptacle, both during cleaning of the surroundings and self cleaning of the filter apparatus and which is easily disposable thereafter.
It is a still further object of the present invention to provide a filter and particularly an initial filter medium in a multi-stage vacuum or suction cleaning arrangement, which filter because of its structure and arrangement periodically cleans itself without interrupting the cleaning cycle and without removing all the dust accumulation and seriously interfering with the efficiency of the filtering cycle.
It is a still further object of the invention to provide a multi-stage vacuum system with very superior and enhanced efficiency due to the incorporation of a filter medium having self-cleaning characteristics and from which the filtered dust may be conveniently and efficiently removed without contamination of the immediate environment.
Other objects and advantages of the vacuum of the invention will become evident from the following description and drawings.